Tundish vessels in the iron and steel industry are used to process (i.e. purify) molten iron or steel at temperatures up to about 3300.degree. F. The molten metal enters the vessel at a location known as the "pouring region" or "impact region." From there, the molten metal is caused to flow toward one or more drains in the floor of the tundish vessel at locations remote from the pouring region. The flow is regulated so that the molten metal has an average "residence time" in the vessel sufficient to allow impurities in the molten metal to rise to the top of the vessel before the molten metal exits through the drains. This can be accomplished using baffles, dams, weirs, and other flow control devices strategically positioned between the pouring region and the drains.
In order to withstand the continuous exposure to hot molten metal, steel tundish vessels are lined on the inside with a high temperature-resistant refractory insulating material that is also resistant to oxidation, corrosion and erosion. The refractory lining can be made from one or more castable refractory materials known in the art including, for example, refractory fibers (e.g. aluminum silicate, calcium silicate), refractory fillers (e.g. alumina, silica, silicates, magnesia), and binder (e.g. colloidal silica, sodium silicate, starch, phenol-formaldehyde resin, urea formaldehyde resin). Eventually, these refractory lining materials wear out, causing the need for repair or replacement.
In some areas of the tundish, including the drain, the refractory materials are exposed to comparatively greater stresses than in the main body of the tundish. At the drains, the velocity of the molten metal is faster than in the main body because a relatively large volume of steel is being channeled through comparatively small openings which cover only a minor portion of the surface area on the tundish floor. As a consequence, the refractory material which protects the drain regions wears out more quickly than the refractory material covering most of the tundish vessel.
In the past, a special procedure has been employed for placing and replacing refractory material in the drain regions of tundish vessels. At the outset, a large circular depression or opening (for example, a depression having a diameter three times the diameter of the drain) is present in the refractory lining surrounding the drain. A refractory drain nozzle was positioned in the drain opening in the steel shell, extending upward into the center of the larger circular depression in the refractory lining. Then, the space between the refractory drain nozzle and the refractory lining (constituting about two-thirds of the diameter of the depression in the refractory lining) was filled with a refractory ramming material using a conventional ramming process.
The ramming process was very labor-intensive and time consuming, requiring as much as 400 lbs. of ramming material. Every time the "rammed" area around the drain became worn or damaged, the entire block of ramming material had to be removed, and the ramming process repeated. This procedure was expensive and required significant "down time" during which the tundish vessel could not be used.
Also, the block of ramming material, once installed, was essentially flush with the tundish floor. In effect, there was no obstruction to prevent heavy impurities on the floor of the tundish from passing through the drain.